package org.greenplum.pxf.plugins.json;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.RecordReader;
import org.greenplum.pxf.plugins.json.parser.PartitionedJsonParser;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

/**
 * Multi-line json object reader. JsonRecordReader uses a member name (set by the <b>IDENTIFIER</b> PXF parameter) to
 * determine the encapsulating object to extract and read.
 * <p>
 * JsonRecordReader supports compressed input files as well.
 * <p>
 * As a safe guard set the optional <b>MAXLENGTH</b> parameter to limit the max size of a record.
 */
public class JsonRecordReader implements RecordReader<LongWritable, Text> {

    public static final String RECORD_MEMBER_IDENTIFIER = "json.input.format.record.identifier";
    public static final String RECORD_MAX_LENGTH = "multilinejsonrecordreader.maxlength";
    private static final Log LOG = LogFactory.getLog(JsonRecordReader.class);
    private final String jsonMemberName;
    private CompressionCodecFactory compressionCodecs = null;
    private long start;
    private long pos;
    private long end;
    private int maxObjectLength;
    private InputStream is;
    private PartitionedJsonParser parser;

    /**
     * Create new multi-line json object reader.
     *
     * @param conf  Hadoop context
     * @param split HDFS split to start the reading from
     * @throws IOException IOException when reading the file
     */
    public JsonRecordReader(JobConf conf, FileSplit split) throws IOException {

        this.jsonMemberName = conf.get(RECORD_MEMBER_IDENTIFIER);
        this.maxObjectLength = conf.getInt(RECORD_MAX_LENGTH, Integer.MAX_VALUE);

        start = split.getStart();
        end = start + split.getLength();
        final Path file = split.getPath();
        compressionCodecs = new CompressionCodecFactory(conf);
        final CompressionCodec codec = compressionCodecs.getCodec(file);

        // openForWrite the file and seek to the start of the split
        FileSystem fs = file.getFileSystem(conf);
        FSDataInputStream fileIn = fs.open(split.getPath());
        if (codec != null) {
            is = codec.createInputStream(fileIn);
            start = 0;
            end = Long.MAX_VALUE;
        } else {
            if (start != 0) {
                fileIn.seek(start);
            }
            is = fileIn;
        }
        parser = new PartitionedJsonParser(is);
        this.pos = start;
    }

    /*
     * {@inheritDoc}
     */
    @Override
    public boolean next(LongWritable key, Text value) throws IOException {

        while (pos < end) {

            String json = parser.nextObjectContainingMember(jsonMemberName);
            pos = start + parser.getBytesRead();
            if (json == null) {
                return false;
            }

            long jsonStart = pos - json.getBytes(StandardCharsets.UTF_8).length;

            // if the "begin-object" position is after the end of our split, we should ignore it
            if (jsonStart >= end) {
                return false;
            }

            if (json.length() > maxObjectLength) {
                LOG.warn("Skipped JSON object of size " + json.length() + " at pos " + jsonStart);
            } else {
                key.set(jsonStart);
                value.set(json);
                return true;
            }
        }

        return false;
    }

    /*
     * {@inheritDoc}
     */
    @Override
    public LongWritable createKey() {
        return new LongWritable();
    }

    /*
     * {@inheritDoc}
     */
    @Override
    public Text createValue() {
        return new Text();
    }

    @Override
    public long getPos() throws IOException {
        return pos;
    }

    /*
     * {@inheritDoc}
     */
    @Override
    public synchronized void close() throws IOException {
        if (is != null) {
            is.close();
        }
    }

    /*
     * {@inheritDoc}
     */
    @Override
    public float getProgress() throws IOException {
        if (start == end) {
            return 0.0f;
        } else {
            return Math.min(1.0f, (pos - start) / (float) (end - start));
        }
    }
}
